Method for the preparation of neutral alkyl esters of phosphoric acid



Patented May 23, 1950 TENT OFFICE METHOD FOR. THE PREPARATION: OF NEUI- TRAL AGID ALKYL ESTERS QF PHOSPHORIG David 0. Hull and Jerry R. Snodgrass, Kingsport, Tenn, assignors t'o Eastman Kodak Company, RochestenN; Y'.,. a; corporation. ofNew.-.lersey No.- Drawing. Application February- 21,1947, Serial No. 731,425

14' Claims;

This invention relates to the preparation of neutral esters of'phosphori'c acid'by thereacti'on ofPzOs-with an alkyl ether in the presence of an olefin. This application is a continuation in'part of our application Serial No. 7113812, filed NO?- vember 22, 1946.

' we have recently shown in our- Patent- No. 24407379, that neutral esters of phosphoric acid may" be prepared by the reaction. of P205 with diethyl" ether at anelevated temperature. The

'reaction Wh-ich .occurs may be represented by the This reaction involves aconsiderable lessening offvolume at the temperature employed; Consequently; it is desirable to maintain pressure in the vessel inwhich thereaction -is carried out; In our Patent No. 2,407,279, wedemonstrated that e the use of the ether in large excess was desirable, this beingforthe purpose of maintaining a suitable. pressure for the reaction. We have now iound an improvementin this process in that the addition of" an olefin; or olefins' with other gases to the reactionvessel providesadesiiable pressure throughout the reaction and contributes to an 7 increased conversion per batchand'a decrease in thee-amount of residue which is obtained.

One object of our invention-is to providean improved method of making trialkyl phosphates. Another'object of our invention. is to provide a method for making trialkyliphosphates.giving:an increased: yield over'prior' methods. A further obiecnofaour invention is to provide a method of making trialkyl phosphatesrusing P205. and alkyl others. A, still further; obiectof. our; invention iseto provide a method of making;trialky1- phosphates-imwhich, an olefingaseous, at. the temperion of the must be discarded. We have found that the;.a'd.-. 5

dition of ethylene tothe reaction vessel so as to providepressure therein tends to diminish the dehydration of the ether and also acts to suppress decomposition of the partial phosphate esters which are present in the residue obtained'. In addition the ethylene present in the masshas a mass action effect, and, therefore, increases the stability ofthe reaction mixture. Therefore; instead' of free phosphoric acidsbeing formed from partialphosphate esters which might be" present, such as diethyl metaphosphate, those est'ers react with ether to form triethyl phosphate; Also, any tetraethyl pyrophosphates which are formed are protected against decomposition and are converted to triethyl phosphate. 'I'he'formation of those intermediateproducts' in this reaction and their conversion to triethyl phosphate are taught in our prior Patent No. 2,407,279, and the disclosure of that patent is=to be considered aspart of the disclosure ofthis application.

The procedure in accordance with ourinvention is useful inthe preparation of trialkyl phos phates of'the alkyls of 2 to 8 carbon'atoms, such as triethyl' phosphate, tri N propyl phosphate,

. tri-isobutyl phosphate, tri N '-butyl-=phosphate', triamyl phosphate, and the like. The process described; however, is particularly: useful in the preparation of triethyl phosphate; To prepare those esters the corresponding others will be reacted with P205 either: with or without catalyst,

asidesired.

In its broadest aspects our invention involves themiX-ing. together of. P205 and the ether in an agitated pressure vessel whereupon the desired amount of olefin is charged to the pressure'vessel which'is then heated at 65-186. C. Although any percentage. of. olefinistuseful inuthe process-it is desirableathat the proportion of olefin used boat 1eastr3%-, basedonthe weight of the reactants. The preferred. amount of olefin to be employed. is withinthe; range of 3.-20%- of; the total. weight: of reactants, although. here againhig'her amounts of olefin may be. used although. there is. no ads vantagezincemploying more than 20 of this ma terial. ZtJis also desirable that thetemperature of the reaction be kept so as. not to. exceed. 180 C. as. much. above that temperature decomposit tion products areaiormedand a1so',..e2zcessive pres.- sures develop in. the reaction vessel. Ifdesired', the: olefin'may be incorporated'in reaction. by using an other solution thereof orraz rosidne'ironz a. previous; batch which. has been saturated olefin, The. preferred, temperature for; the: carrying cutoff the. reaction is-withina therrange-of 140-180 C. The highest yie1dsare obtainedwhen the residue of a previous batch is included in the mixture of the reaction ingredients.

Included within the scope of this invention is not only the reaction of P205 and ether having alkyls of 2-8 carbon atoms but also the reaction of intermediate products, such as dialkyl metaphosphate or tetra alkyl pyrophosphate, or both, with ether to form more trialkyl phosphate than was formed in the process in which these intermediate products were obtained. The reaction in accordance with our invention may be carried out either with or without catalyst, as desired by the individual operator. Some of the catalysts which have been found useful in this reaction are the halogens, boron trifluoride etherate, halogen acids, as well as other esterification catalysts, some of which are listed in our Patent No.

2,407,275. If desired, inert organic solvents may be employed as diluents although it has been found that the reaction goes very well both without diluents and without catalysts, other than than those which are necessary to the invention.

It is desirable in carrying out the reaction of our invention that the ether employed be at least a theoretical amount based on the P205. t is preferable that the ether be used in an amount at least three times the molar amount of P205 or even more, particularly in those cases where an inert solvent is not employed. The amount of ether used, however, need not be as great as that employed in our prior patent in view of the presence of olefin in the reaction vessel. We have found that the reaction in accordance with our invention proceeds very well with the use of 3-5 moles of ether to one mole of P205.

The reaction of our invention is carried out in an enclosed vessel and, therefore, is under pressure. The pressures which are employed are the result of the temperature used and are not critical except that the vessel employed should be gastight so that the pressure generated by ,the temperature used will be present during the reaction. Ordinarily the olefin is introduced into the autoclave under pressure so that initially the pressure therein is decidedly above atmospheric even before the heating of the vessel takes place.

The following examples illustrate our invention:

Example 1.A stirrer type copper lined autoclave was charged with 2960 g. of diethyl ether and 1420 g. of P205. 280 g. of ethylene were introduced, and the mixture was autoclaved at 170-180 C. for eight hours whereupon the reaction was substantially completed. The ethylene and excess ether which were in gas form were then led off from the autoclave and the ether was condensed, the ethylene being returned to a gas holder. The mass obtained was then distilled at reduced pressure (2-5 mm. of mercury). The distillation was discontinued when the temperature of the base heater had reached 180 C. 2250 g. of triethyl phosphate (62% yie1d,'based on the P205) were obtained and a residue weighing 1400 g. remained.

Example 2.+The residue from Example 1 was mixed with 2960 g. of diethyl ether and 1130 g. of P205 in'an autoclave. Ethylene was forced into the autoclave until a pressure of 500 p. s. i. was obtained. The mixture was autoclaved at 165 C. for eight hours. The reaction mass obtained was treated as in Example 1 and 2635 g. of triethyl phosphate were obtained. A yield of 89%, based on the P205 was obtained, and the residue remaining weighed 1465 g.

Example 3.2160 g. of diethyl metaphosphate were mixed with 1500 g. of diethyl ether in the autoclave. The pressure in the autoclave was brought up to 500 p. s. i. with ethylene. The mixture was autoclaved at -170 C. for ten hours. The ethylene and ether in gaseous form were drawn off and recovered. The reaction mass was vacuum distilled from which was obtained 1402 g. of triethyl phosphate, representing a yield of 75 based on the diethyl metaphosphate.

Example 4.--The procedure described in Example 1 was repeated except that di-isopropyl ether was employed instead of the diethyl ether. The ethylene and'ether in gaseous form were drawn off and recovered, and the reaction mass was vacuum distilled to separate the tri-isopropyl phosphate obtained and the residue of partial phosphate esters.

Example 5.4000 parts of di-isopropyl ether and 1420 parts 0f-P205 were mixed together in a. stirrer type copper-lined autoclave. The auto;- cl-ave was charged to 560 p. s. i. with a mixture of crude refinery gas containing methane, 0.6 mol. percent; ethylene, 2.1 mol. percent; ethane, 5.3 mol. percent; propylene, 56.0 mol. percent, and propane, 35.9 mol. percent. The mass was slowly heated to -1'70 C. and autoclaved for eight hours to complete the reaction. The olefin-inert gas and excess ether which were in gas form were led off from the autoclave, and the ether was condensed, the gas being conducted to a gas holder. The mass was then distilled at reduced pressure. 2600 parts of triisopropyl phosphate were obtained.

Example 6.-The procedure of the preceding example was repeated except that diethyl ether was employed instead of di-isopropyl ether. The triethyl phosphate obtained was separated from the remainder of the mass by vacuum distillation to obtain a 59% yield.

Example 7.-A copper-lined autoclave was charged with 350 parts of diamyl ether, 71 parts of P205 and 40 parts of amylene. The autoclave was heated to 60-70 C. for one hour where the reaction heat carried the temperature to 90 C. The mixture was slowly heated to 160-170" C. and autoclaved for eight hours to complete the reaction. Distillation at reduced pressure gave 205 parts of tri-N-amyl phosphate.

Example 8.-The procedure of the preceding example was repeated but using di-Z-ethyl hexyl ether and P205 as the reactants. 2-ethyl hexene-l was used as the olefin. A 38% conversion to tri-Z-ethyl hexyl phosphate was obtained.

The trialkyl phosphates obtained in accordance with the process of our invention are of good quality and are useful in the various procedures in which trialkyl phosphates have been employed heretofore as listed in previous disclosures.

In the process in accordance with our invention the olefin which is employed should be gaseous at the temperature at which the reaction occurs, particularly the last portion of the reaction. The choice of olefin to be employed depends upon the temperature conditions to be used and to some extent upon the reactants. Olefins which may be employed in reactions in accordance with our invention, providing, of course, the temperatures are sufici'ently high to create pressure in the autoclave are methylene, ethylene, propylene, butylene, amylene, and the like.

We claim:

1. The method of preparing a trialkyl phosphate which comprises reacting phosphorus pent oxide with an ether having only alkyl groups of 2-8 carbon atoms in an enclosed vessel at a tem perature of 65-180 C. in an atmosphere of olefin gaseous at the temperature of the reaction, the olefin being at least 3% by weight of the re-- actants, all for a sufficient time to cause the formation of a substantial proportion of trialkyl phosphate.

2. A method of preparing triethyl phosphate which comprises reacting phosphorus pentoxide with diethyl ether in an enclosed vessel at a temperature of 65-180 C. while contacted with ethylene, the ethylene being at least 3% by weight of the reactants, for a sufficient time to cause the formation of a substantial proportion of triethyl phosphate.

3. A method of preparing triethyl phosphate which comprises reacting phosphorus pentoxide with diethyl ether in an enclosed vessel at a temperature of 65-180 C. while in contact with ethylene, the ethylene being at least 3% by weight of the reactants, for a sufficient time to result in the formation of a substantial amount of triethyl phosphate, followed by separation of the triethyl phosphate from the mass by vacuum distillation.

4. A method of preparing triethyl phosphate which comprises reacting phosphorus pentoxide with diethyl ether in an enclosed vessel at a. temperature of 65-l80 C. while contacted with ethylene, the ethylene being at least 3% by weight of the reactants, for a suflicient time to give a substantial amount of triethyl phosphate, followed by separation of the triethyl phosphate from the mass by vacuum distillation and mixing the residue therefrom with diethyl ether and again subjecting to a temperature of 65-180 C. while in contact with ethylene to obtain a fur- V ther amount of triethyl phosphate.

5. A method of preparing triethyl phosphate which comprises reacting phosphorus pentoxide with diethyl ether in an enclosed vessel at a temperature of Mil-180 C. while in contact with ethylene, the ethylene being at least 3% by weight of the reactants, for a sufficient time to result in a substantial proportion of triethyl phosphate.

6. A method of preparing triethyl phosphate which comprises reacting an ethyl metaphosphate with diethyl ether in an enclosed vessel at a temperature of 65-180 C. while in contact with ethylene, the ethylene being at least 3% by weight of the reactants, for a sufficient time to cause the formation of a substantial proportion of triethyl phosphate.

7. A method of preparing triethyl phosphate which comprises reacting diethyl ether with tetraethyl pyrophosphate in an enclosed vessel at a temperature of 65-180 C. while in contact with ethylene, the ethylene being at least 3 by weight of the reactants, for a suflicient time to cause the formation of a substantial proportion of triethyl phosphate.

8. A method of preparing triethyl phosphate which comprises reacting phosphorus pentoxide with diethyl ether at a temperature of 65-180 C. in an enclosed vessel also containing an olefin gaseous at the temperature of the reaction, the olefin being at least 3% by weight of the reactants, for a sufiicient time to cause the formation of a substantial proportion of triethyl phosphate.

9. A method of preparing triethyl phosphate which comprises reacting phosphorus pentoxide with diethyl ether at a temperature of 65-180" C. in an enclosed vessel containing a substantial proportion of a mixture of olefins and inert gases, the olefin amount being at least 3% by weight of the reactants for a suificient time to result in the formation of a substantial proportion of triethyl phosphate.

10. A method of preparing a trialkyl phosphate which comprises reacting phosphorus pentoxide with an ether having only alkyl groups of 2 carbon atoms in an enclosed vessel at a temperature of 65-180 C. in an atmosphere of ethylcue, the ethylene being at least 3% by weight of the reactants, for a sufiicient time to cause the formation of a substantial proportion of trialkyl phosphate.

11. A method of preparing a trialkyl phosphate which comprises reacting phosphorus pentoxide with an ether having only alkyl groups of 2-8 carbon atoms in an enclosed vessel at a temperature of 65-180 C. in an atmosphere of amylene, the amylene being at least 3% by weight of the reactants, for a sufficient time to cause the formation of a substantial proportion of trialkyl phosphate.

12. A method of preparing a trialkyl phosphate which comprises reacting a dialkyl metaphosphate with an ether having only alkyl groups of 2-8 carbon atoms in an enclosed vessel at a temperature of 65-180 C. in an atmosphere of an olefin gaseous at the temperature of reaction, the olefin being at least 3% by weight of the reactants, for a sufiicient time to cause the formation of a substantial proportion of trialkyl phosphate.

13. A method of preparing a trialkyl phosphate which comprises reacting a tetra alkyl pyrophosphate with an ether having only alkyl groups of 2-8 carbon atoms in an enclosed vessel at a temperature of 65-130 C. in an atmosphere of an olefin gaseous at the temperature of reaction, the

olefin being at least 3% by weight of the reactants, for a suflicient time to cause the formation of a substantial proportion of trialkyl phosphate. 14. A method of preparing a trialkyl phosphate which comprises reacting phosphorus pentoxide with an ether having only alkyl groups of 2-8 carbon atoms in an enclosed vessel at a temperature of 65-180" C. in an atmosphere of an olefin, gaseous at the temperature of reaction, the olefin being at least 3% by weight of the reactants, for a sufiicient time to result in the formation of a substantial proportion of trialkyl phosphate, followed by separation of the trialkyl phosphate from the mass by vacuum distillation.

DAVID C. HULL.

JERRY RANGE SN ODGRASS.

REFERENCES CITED UNITED STATES PATENTS Name Date Hull et a1. Sept. 10, 1946 Number 

1. THE METHOD OF PREPARING A TRIALKYL PHOSPHATE WHICH COMPRISES REACTING PHOSPHORUS PENTOXIDE WITH AN ETHER HAVING ONLY ALKYL GROUPS OF 2-8 CARBON ATOMS IN AN ENCLOSED VESSEL AT A TEMPERATURE OF 65-180*C. IN AN ATOMOSPHERE OF OLEFIN GASEOUS AT THE TEMPERATURE OF THE REACTION, THE OLEFIN BEING AT LEAST 3% BY WEIGHT OF THE REACTANTS, ALL FOR A SUFFICIENT TIME TO CAUSE THE FORMATION OF A SUBSTANTIAL PROPORTION OF TRIALKYL PHOSPHATE. 